Process for the production of photographic reproduction surfaces on aluminium and its alloys



nited States Patent .3 2,710,804 PROCESS FOR THE PRODUCTION OF PHOTO- GRAPHIC REPRODUCTION SURFACES 0N ALUMINIUM AND ITS ALLOYS Max Schenk, Basel, Switzerland, ,assignor to Dr. ,von Giutz & Muller ens se scha t, Ba n, w tzerl nd, a corporation of Switzerland N0 Drawing. Application August 1, 1950, "Serial No. 177,119

C i p y, pp ti nswitz rland Aqgu t .1 4 2 Claims. .(Cl. 95-7) By a known process for producing representations and reproductions of all kinds with the aid of photo-sensitive substances, an adsorbent, oxidic layer, such as is produced by anodic oxidation on aluminium, can be used as the sole carrier for the photo-sensitive substances. Hitherto, essentially, two processes have been proposed and employed for sensitising the anodic film to light. By one process, the porous layer is impregnated with a solution of a substance that is already photo-sensitive, for example a ferric salt, and, by the other process, the photosensitive substance, for example a silver halide, is produced by double decomposition in the film itself. Ifone dispenses with the very limited employment of oxide layers sensitised with iron salts, only the films sensitised with silver halides remain for a wider basis of employment. Double chemical decomposition by-means of pre cipitation reactions, for example with silver nitrate and potassium bromide, has very considerable disadvantages. Thus, in order to incorporate suflicient silver halide, it is necessary to repeat the precipitation reaction a number of times. However, even this would not, in the case of the ordinary anodic films, for example in the case of films produced with direct current in sulphuric-acid solution, lead to the desired object since the volume of their pores would be far too small. A very special process must, therefore, be employed to obtain films with the necessary absorptive power. It has also been attempted to render the ordinary anodic layer more absorbent before sensitising by chemical means or by thermal treatment. Phosphate and fluoride layers have also been proposed as carriers for the photo-sensitive substances. All these expedients lead to layers which do not approach ordinary layers with regard to hardness, resistance to wear, closability of the pores by re-consolidation, surface smoothness and resistance to corrosion. It has also been found that, in the precipitation reactions, the photo-sensitive products are principally deposited at the open ends of the pores--a phenomenon which can be explained by the laws of diffusion and osmosis.

According to the present invention, by means of which the disadvantages hereinbefore mentioned are obviated, a photographic reproduction surface is produced in an adsorbent, firmly adhering aluminum oxide layer by treating the layer with an organic substance which reduces silver compounds to metallic silver, treating the layer with a solution containing a silver compound,thereby to mordant metallic silver .to this layer and, finally, converting the metallic silver into silver halide.

There are a large number of organic compounds capable of reducing silver ions, especially those having the character of a dyestuff, which dye the oxidic layer fast, similarly to the dyeing of wool and cellulose by textile dyestuffs. Among these, there have been found to be specially advantageous, for the process according to the invention, dyestufis having the character of mordants, i. e., dyestuffs which have a certain chemical affinity to aluminum oxide, for example derivatives of anthraquinone (alizarin types), of flavone and xanthone, or derivatives of pyronin (gallein type) and .oxazine (gallocyanin type). In general, it has been found that organic compounds will reduce silver ions to metallic silver when, at least, two hydroxy or amino groups are in the ortho .or para position to each other in the ring system or-when a reactive aldehyde group is contained in the molecule.

The following are mentioned as examples .of suitable organic compounds:

1 1 8- etrahyd oxy n hr qu n n OH A \QQ/ \OH OH DihydroXy-fiuorescein .(gallein) Gal yan OH CE: 0 v 0 NF? 0 Numerous compounds, chiefly derivatives of benzene or naphthalene, which have hydroxy or amino groups in the ortho or para position, are suitable for impregnating the absorbent, firmly adhering layer with more or less concentrated solutions in water or other solvents. It is especially advantageous to select compounds which are soluble in organic solvents but not in cold water such as, for example, 4-nitro-2-amino-l-phenol, 6-nit-ro-2-arnino- ,phenol-4-sulphonic acid, 4:G-dinitreieminophenol, p-

355 hydroxyphenylglycin, methyl-p-aminophenol, ethyl gallate, gallicanilide.

It has been ascertained by experiments that, for certain purposes, not all anodically producible layers are equivalent. If, for example, the process is to be employed for the production ,of photographic copies on aluminium or aluminium alloys, :the layers must withstand a series of treatments without altering unfavourably. It is necessary that a good absorptive power and photographic capacity, as well as unchangeability should be maintained during the time taken by the treatment. It has been found that, for photographic purposes, suitable layers are produced anodically with the aid of direct current in an aqueous solution which contains free oxalic acid as well as soluble oxalates and has a hydrogen exponent of between pH=l.2 and pH=4.0. Suitable soluble oxalates are those of alkali metals and also those of metals of the titanium group, i. e., titanium, zirconium and thorium. With the former oxalates, clear, colourless, transparent layers are obtained, whilst with the latter oxalates non-transparent, opaque layers are obtained. The advantages of the employment of these layers for the purposes of the present invention are considerable. In addition to a good hardness and resistance to abrasion, they possess a high chemical resistance; they are very porous and absorbent and can very easily be dyed. On closing the pores by means of the usual warm, aqueous solutions, their surface becomes glass-hard and unsoilable.

The reaction of the organic substance, deposited in the layer, with solutions containing silver in the form of ions is advantageously carried out by immersing the suitably pretreated article in the reactive silver solution; the latter may have a slightly acid, a neutral or a slightly alkaline reaction according to the reactivity of the organic substance. Ammoniacal silver solutions, preferably those having no or only a slight content of ammonia, have been found to be advantageous and usable in most cases. temperature of and the time taken by this immersion treatment depend upon the nature of the layer and upon the kind of organic substance. Advantageously, the organic substance selected is a substance the oxidation products of which can be dissolved out without trouble from the absorbent layer on the reduction of the silver salt, so that none of them remain behind in the layer.

The metallic silver precipitated in the layer is present in an ultramicroscopically fine state. It can readily be reoxidised to a silver compound. Thus, according to the present invention, it is easily possible to convert the metallic silver into a photo-sensitive silver halide by immersing the article provided with the silver-containing layer either in a solution containing at least one oxidising agent and one or more halides or by exposing it to a damp atmosphere which contains at least one halogen element (chlorine gas etc.). If silver chloride has been produced in this way, it can be converted wholly or partially into the corresponding bromide or iodide by treatment with solutions of bromides or iodides. ble to vary photo-sensitivity in wide limits. Such prepared articles, for example sheets of metal, can be employed in a similar manner for photographic purposes, e. g., as photographic plates on glass or as prepared films or papers. photographic negative and developed in a suitable mineral or organic developer; the pictures produced may be toned, intensified, reduced and fixed in the known manner. It is also possible to after-treat the oxidic layer in the known manner after finishing the photographic representation, i. e., by colouring it or recompressing it or to thicken the silver image to produce relief by galvanic plating,

Example I A solution of 3000 gms. of potassium oxalate in 100 litres of water is prepared. Oxalic acid is then dissolved therein until the solution has a hydrogen exponent of pH=2.8. In the solution, heated to 55 C., an aluminium sheet is treated, with movement of the liquid,

anodically with a current density of 2.0 amperes per The In this way, it is possi- They may be exposed beneath a suitable S-amino-salicylic acid and resorcin. The dyestuti goes on in the layer with a red colour. After rinsing in water, the sheet coloured in this manner is immersed for one hour in a solution at 45 C. which contains gms. of silver nitrate in 1 litre of water and as much ammonia as is just necessary for the formation of silver-ammonia nitrate. A black coloration having an excellent fastness to light and weather is produced. By converting the metallic silver into silver halide, a photographic material for copying purposes is obtained.

Example 2 A sheet of pure aluminium is anodically treated with a current density of 2 amperes per square decimetre in the following solution at 58 C. with direct current for 35 minutes. The solution is produced by dissolving 2000 gms. of the double salt titanium-potassium oxalate in 100 litres of water and adding oxalic acid until the hydrogen exponent of the solution corresponds to pH=2.l. The layer obtained in this way is non-transparent and of a whitish light grey. Instead of the sheet, finished shaped articles or parts thereof or pieces produced from profiles may be employed. After rinsing, the sheet etc. is treated in a solution at 60 C. of gms. of l:5-dihydroxy-4 8-diaminoanthraquinone-2: 6-disulphonic acid in 1 litre of water until a deep blue coloration, which is fast to water, is produced. The sheet etc. is then allowed to react with a solution of gms. of silver-ammonia nitrate in 1 litre of water at C. for 3 hours, the colour changing from blue into a deep black. The object is now immersed in a solution of 10 gms. of sulphuric acid, 2 gms. of potassium permanganate and 15 gms. of sodium chloride in 1 litre of water until it has become white. This treatment is carried out in red light. After thoroughly rinsing in water and after drying, the sheet etc. is exposed beneath a transparent photo graphic negative, developed in a photographic developer, toned in a gold toning bath, fixed and rinsed. Finally, for the purpose of closing the pores, it is after-treated in a hot solution of a nickel salt or in boiling Water. A photographic copy of a clear effect which is rich in contrasts is produced.

Example 3 A sheet of pure aluminium 0.25 mm. thick is anodised for 35 minutes in an aqueous solution, free from sulfuric acid, of 6% of chromic acid and 1% of titaniumpotassium oxalate at C. with a current density of 1 ampere per square decimetre. The whitish oxide layer produced is then dyed violet in a 1% solution of dihydroxyfiuorescein (gallein). By reacting the dyestufi in a solution of 20 gms. per litre of silver-ammonia nitrate, a deep black coloration is produced by the occluded, finely divided metallic silver. The sheet is then exposed, in a closed vessel at dark-room illumination or in the dark, to the action of a damp atmosphere containing elementary chlorine gas. In this way, the silver is oxidised to silver chloride. As soon as all the silver has been converted, as can easily be ascertained by the whitish colour, the sheet is first rinsed with a very dilute solution of sodium carbonate and then with clean water and allowed to dry. The sheet prepared in this way is excellently suitable, especially in conjunction with an acid, so-called physical developer, for the production of black-andavhite reproductions, for example for the photographic reproduction of cards and incombustible documents or for the production of sign-boards and absolutely correct scales and rules.

The examples given represent a few possible methods of applying and carrying out the subject matter of the invention and the scope of the invention is not limited by them.

What I claim is:

l. A method of producing a photographic reproduction surface comprising the steps of providing an adsorbent, firmly adhering aluminum oxide layer on an aluminum or aluminum alloy base by subjecting the aluminum or aluminum alloy base to anodic oxidation with direct current in an aqueous solution containing free oxalic acid and an alkali oxalate, said solution having a pH between about 1.2 and 4.0; treating the aluminum oxide layer with a first solution containing an organic reducing agent capable of reducing silver compounds and of being mcrdanted to the aluminum oxide layer; treating the layer with a second solution containing a silver compound reducible by said reducing agent, thereby to mordant metallic silver to the oxide layer; and then treating the layer with an acid aqueous medium containing at least one free halogen until the conversion of the metallic silver into silver halide is completed.

2. A method of producing a photographic reproduction surface, comprising the steps of providing an adsorbent, firmly adhering aluminum oxide layer on an aluminum or aluminum alloy base by subjecting the aluminum or aluminum alloy base to anodic oxidation with direct current in an aqueous solution containing free oxalic acid and an oxalate of the titanium group, said solution having a pH between about 1.2 and 4.0; treating the aluminum oxide layer with a first solution containing an organic reducing agent capable of reducing silver compounds and of being mcrdanted to the aluminum oxide layer; treating the layer with a second solution containing a silver compound reducible by said reducing agent, thereby to mordant metallic silver to the oxide layer; and then treating the layer With an acid aqueous medium containing at least one free halogen until the conversion of the metallic silver into silver halide is completed.

References Cited in the file of this patent UNITED STATES PATENTS 1,735,509 Setoh et al. Nov. 12, 1929 1,962,339 Cotton June 12, 1934 1,988,012 Mason Jan. 15, 1935 2,115,339 Mason Apr. 26, 1938 2,253,070 Evans Aug. 19, 1941 2,320,005 Michaelis May 25, 1943 2,543,691 Friedman Feb. 27, 1951 OTHER REFERENCES Organic Compounds Suggested for Photographic Development, pages 329333 of Handbook of Photography; Henney and Dudley, 1939, McGraW-Hill, New York. 

1. A METHOD OF PRODUCING A PHOTOGRAPHIC REPRODUCTION SURFACE COMPRISING THE STEPS OF PROVIDING AN ADSORBENT, FIRMLY ADHERING ALUMINUM OXIDE LAYER ON AN ALUMINUM OR ALUMINUM ALLOY BASE BY SUBJECTING THE ALUMINUM OR ALUMINUM ALLOY BASE TO ANODIC OXIDATING WITH DIRECT CURRENT IN AN AQUEOUS SOLUTION CONTAINING FREE OXALIC ACID AND AN ALKALI OXALATE, SAID SOLUTION HAVING A PH BETWEEN ABOUT 1.2 AND 4.0. TREATING THE ALUMINUM OXIDE LAYER WITH A FIRST SOLUTION CONTAINING AN ORGANIC REDUCING AGENT CAPABLE OF REDUCING SILVER COMPOUNDS AND OF BEING MORDANTED TO THE ALUMINUM OXIDE LAYER, TREATING THE LAYER WITH A SECOND SOLUTION CONTAINING A SILVER COMPOUND REDUCIBLE BY SAID REDUCING AGENT, THEREBY TO MORDANT METALLIC SILVER TO THE OXIDE LAYER; AND THEN TREATING THE LAYER WITH AN ACID AQUEOUS MEDIUM CONTAINING AT LEAST ONE FREE HALOGEN UNTIL CONVERSION OF THE METALLIC SILVER INTO SILVER HALIDE IS COMPLETED. 